Base station with rapid handover function of a cellular TDMA/FDMA mobile radio system, particularly of a cellular DECT system

ABSTRACT

In order that a mobile part having a slow channel changing function can be synchronized in a manner which is economic in terms of frequencies and, at the same time, to at least two base stations having a fast channel changing function in a cellular TDMA/FDMA radio system, in particular in a cellular DECT/GAP system, the base station transmits broadcast information to the mobile part. The mobile part maintains a telecommunications link to one of the base stations in the radio system, using a predetermined transmit separation which is defined as a number of TDMA time slots and is greater than a receive separation which is predetermined by the slow channel changing function of the mobile part and is defined as a number of TDMA time slots.

BACKGROUND OF THE INVENTION

In communication systems having a communication transmission pathbetween a communication source and a communication sink, transmittingand receiving devices are used for communication processing andtransmission in which

1) the communication processing and communication transmission can takeplace in a preferred transmission direction (simplex operation) or inboth transmission directions (duplex operation),

2) the communication processing is analogue or digital,

3) the communication transmission via the long-distance transmissionpath takes place wire-free on the basis of various communicationtransmission methods FDMA (Frequency Division Multiple Access), TDMA(Time Division Multiple Access) and/or CDMA (Code Division MultipleAccess) for example in accordance with radio standards such as DECT,GSM, WACS or PACS, 1S-54, PHS, PDC etc. (see IEEE CommunicationsMagazine, January 1995, pages 50 to 57; D. D. Falconer et al: “TimeDivision Multiple Access Methods for Wireless Personal Communications”)and/or by wire.

“Communication” is a generic term which covers both the message content(information) and the physical representation (signal). Despite acommunication having the same message content—that is to say the sameinformation—different signal forms may occur. Thus, for example, acommunication relating to an item may be transmitted in any of thefollowing forms

(1) an image,

(2) as the spoken word,

(3) as the written word,

(4) as an encrypted word or image.

The type of transmission according to forms (1), (2) and (3) is in thiscase normally characterized by continuous (analogue) signals, while thetype of transmission according to forms (4) normally takes place bymeans of discontinuous signals (for example pulses, digital signals).

On the basis of this general definition of a communication system, theinvention relates to a base station having a fast channel changingfunction in a cellular TDMA/FDMA radio system, in particular in acellular DECT system.

A cellular radio system, as a subset of the previously definedcommunication system is, for example, the cellular DECT-System (DigitalEnhanced (previously: European) Cordless Telecommunication; see (1):Nachrichtentechnik Elektronik 42 (Electronic telecommunication 42)(1992) January/February No. 1, Berlin, DE: U. Pilger “Struktur desDECT-Standards” (Structure of the DECT Standard), pages 23 to 29 inconjunction with the ETSI Publication ETS 300175-1 . . . 9, October1992; (2): Telcom Report 16 (1993), No. 1, J. H. Koch: “DigitalerKomfort für schnurlose Telekommunikation—DECT-Standard eröffnet neueNutzungsgebiete” (Digital convenience for cordlesstelecommunications—DECT Standard opens up new application areas), pages26 and 27; (3): tec 2/93—the Technical Magazine from Ascom “Wege zuruniversellen mobilen Telekommunikation” (Universal mobiletelecommunication techniques), pages 35 to 42; (4): PhilipsTelecommunication Review, Vol. 49, No. 3, September 1991, R. J. Mulder:“DECT, a universal cordless access system”; (5): WO 93/21719 (FIGS. 1 to3 with associated description)) or the cellular GAP-System (GenericAccess Profile; ETSI-Publikation prETS 300444, April 1995, Final Draft,ETSI, FR), which may be designed, for example, on the basis of amonocellular DECT/GAP system (Single Cell System) according to FIG. 1and in accordance with the illustration in FIGS. 4 and 5.

According to the DECT/GAP Standard and in accordance with theillustration in FIG. 1, a DECT/GAP radio interface which is designed forthe frequency band between 1.88 and 1.90 GHz can be used to set up on aDECT/GAP base station BS a maximm of 12 links, using the TDMA/FDMA/TDDmethod (Time Division Multiple Access/Frequency Division MultipleAccess/Time Division Duplex) in parallel with DECT/GAP mobile parts MT1. . . MT12. The figure of 12 results from a number “kg” of time slots ortelecommunications channels available for duplex operation of a DECT/GAPsystem (k=12). The links may in this case be internal and/or external.In the case of an internal link, two mobile parts which are registeredat the base station BS, for example the mobile part MT2 and the mobilepart MT3, can communicate with one another. In order to set up anexternal link, the base station BS is connected to a telecommunicationsnetwork TKN, e.g. in cable form via a telecommunications line unit TAE,or a private branch exchange is connected to a cable telecommunicationsnetwork, or (according to PCT Reference WO 95/05040 in wire-free form asa repeater station) to a higher-level telecommunications network. In thecase of the external link, it is possible to communicate with a mobilepart, for example with a mobile part MT1, via the base station BS andthe telecommunications line unit TAE, or for the private branch exchangeNStA to communicate with a subscriber in the telecommunications networkTKN. If—as in the case of Gigaset 951 (Siemens cordless telephone, seeTelcom Report 16, (1993) Issue 1, pages 26 and 27)—the base station BShas only one connection to the telecommunications line unit TAE or tothe private branch exchange NStA, then only one external link can be setup. If—as in the case of Gigaset 952 (Siemens cordless telephone; seeTelcom Report 16, (1993), Issue 1, pages 26 and 27)—the base station BShas two connections to the telecommunications network TKN then, inaddition to the external link to the mobile part MT1, a further externallink is possible from a cable telecommunications terminal TKE connectedto the base station BS. In this case it is also in principle feasiblefor a second mobile part, for example the mobile part MT12, to use thesecond connection for an external link, instead of thetelecommunications terminal TKE. While the mobile parts MT1 . . . MT12are operated using a battery or a rechargeable battery, the base stationBS, which is designed as a small cordless exchange, is connected to avoltage network SPN via a network interface unit NAG.

Based on the document Components 31 (1993), Issue 6, pages 215 to 218;S. Althammer, D. Brückmann: “Hochoptimierte IC's fürDECT-Schnurlostelefone” (Highly optimized ICs for DECT cordlesstelephones), FIG. 2 shows the basic circuit design of the base stationBS and of the mobile part MT according to FIG. 1. According to thisfigure, the base station BS and the mobile part MT have a radio part FKTwith an antenna ANT used for transmitting and receiving radio signals, asignal processing device SVE and a central controller ZST, which areconnected to one another in the illustrated manner. The radio part FKTessentially contains the known devices such as the transmitter SE, thereceiver EM and the synthesizer SYN. The signal processing device SVEcontains, inter alia, a coding/decoding device CODEC. Both for the basestation BS and for the mobile part MT, the central controller ZST has amicroprocessor μP with a program module PGM designed in accordance withthe OSI/ISO layer model (see (1): Instruction Sheets—Deutsche Telekom,Year 48, 2/1995, pages 102 to 111; (2): ETSI Publication ETS 300175-1 .. . 9, October 1992), a signal control section SST and a digital signalprocessor DSP, which are connected to one another in the illustratedmanner. Of the layers defined in the layer model, only the first fourlayers, which are absolutely essential for the base station BS and forthe mobile part MTλ are illustrated. The signal control section SST inthe base station BS is designed as a Time Switch Controller TSC, andthat in the mobile part MT is designed as a Burst Mode Controller BMC.The major difference between the two signal control sections TSC, BMC isthat the base-station-specific signal control section TSC also carriesout switching functions that the mobile-part-specific signal controlsection BMC does not.

The basic method of operation of the circuit units mentioned above isdescribed, for example, in the document cited above, Components 31(1993), Issue 6, pages 215 to 218.

The circuit layout described according to FIG. 2 is supplemented byadditional functional units in the base station BS and in the mobilepart MT in accordance with their function in the DECT/GAP systemaccording to FIG. 1.

The base station BS is connected to the telecommunications network TKNvia the signal processing device SVE and the telecommunications lineunit TAE or the private branch exchange NStA. As an option, the basestation BS may also have an operator interface (functional units showndashed in FIG. 2) which, for example, comprises an input device EEdesigned as a keyboard, an indicator device AE designed as a display, aspeech/listening device SHE designed as a handset with a microphone MIFand a listening capsule HK, as well as a bell TRK.

The mobile part MT has the operator interface which may be used as anoption for the base station BS, with the control elements describedabove associated with this operator interface.

Based on the document “Nachrichtentechnik Elektronik 42” (Electronictelecommunications 42) (1992) January/February, No. 1, Berlin, DE; U.Pilger: “Struktur des DECT-Standards” (“Structure of the DECTStandard”), pages 23 to 29 in conjunction with ETS 300 175-1 . . . 9,October 1992”, FIG. 3 shows the TDMA structure of the DECT/GAP systemTKS according to FIG. 1. In terms of the multiple access methods, theDECT/GAP system is a hybrid system in which radio messages can betransmitted in a predetermined time sequence from the base station BS tothe mobile part MT and from the mobile part MT to the base station BSusing the FDMA principle at ten frequencies in the frequency bandbetween 1.88 and 1.9 GHz and using the TDMA principle according to FIG.3 (Time Division Duplex operation). The time sequence is in this casegoverned by a multi-time frame MZR which occurs every 160 ms and has 16time frames ZR each with a time duration of 10 ms. Information whichrelates to a C, M, N, P, Q channel defined in the DECT Standard istransmitted separately to the base station BS and the mobile part MT inthese time frames ZR. If information for a number of these channels istransmitted in a time frame ZR, then the transmission takes place inaccordance with a priority list where M>C>N and P>N. Each of the 16 timeframes ZR in the multi-time frame MZR is in turn split into 24 timeslots ZS each having a time duration of 417 μs, of which 12 time slotsZS (time slots 0 . . . 11) are allocated to the transmission direction“base station BS→mobile part MT” and a further 12 time slots ZS (timeslots 12 . . . 23) are allocated to the transmission direction “mobilepart MT→base station BS”. Information with a bit length of 480 bits istransmitted in each of these time slots ZS, in accordance with the DECTStandard. Of these 480 bits, 32 bits are transmitted as synchronizationinformation in a SYNC field and 388 bits as wanted information in a Dfield. The remaining 60 bits are transmitted as additional informationin a Z field and as protection information in a “Guard Time” field. The388 bits which are transmitted as wanted information in the D field arein turn split into a 64-bit long A field, a 320-bit long B field and a4-bit long “X-CRC” word. The 64-bit long A field is composed of an 8-bitlong data header, a 40-bit long data record with data for the C, Q, M,N, P channels and a 16-bit long “A-CRC” word.

On the basis of PCT Reference WO94/10811 (Patent Claims 1 and 2), it ispossible for the base station BS and/or the mobile part MS according toFIGS. 1 to 3 to have a radio part which is able to carry out either afast channel change or a slow channel change. The terms used in thesecases are a “Fast Hopping” radio part (FH radio part) and a “SlowHopping” radio part (SH radio part). In consequence, the base station BSis either an FH base station or an SH base station, and the mobile partis either an FH mobile part or an Sh mobile part.

Based on the DECT/GAP system according to FIG. 1, FIG. 4 shows acellular DECT/GAP multi-system CMI (Cordless Multicell Integration), inwhich a number of the DECT/GAP systems TKS described above are present,each having a base station BS and one or more mobile parts MTconcentrated—in the sense of a “hot spots” arrangement—at any givengeographic location, for example in an administration building withlarge open-plan offices occupying whole floors. Instead of a “closed”geographic location, such as the administration building, an “open”geographic location with strategic telecommunications significance is,alternatively, also possible, for example areas in cities with a highvolume of traffic, a major agglomeration of commercial units and a largeamount of movement by people, for the installation of a cellularDECT/GAP multi-system CMI. Some of the base stations BS arranged in thelarge office are, in contrast to the base stations shown in FIGS. 1 and2, in this case designed in accordance with PCT Reference WO 94/10764 asantenna diversity base stations. The concentration of DECT/GAP systemsTKS is in this case designed (gap-free radio coverage of the geographiclocation) such that individual DECT/GAP systems TKS operate in the samevicinity, with the cellular DECT/GAP radio areas FB overlapping.

The same vicinity can in this case mean, depending on the amount ofoverlapping, that

a) a first base station BS1 in a first telecommunications system TKS1 isarranged in a first radio area FB1 (radio cell), and a second basestation BS2 in a second telecommunications system TKS2 is arranged in asecond radio area FB2 (radio cell) and they can set uptelecommunications links to at least one mobile part MT_(1,2),

b) a third base station BS3 in a third telecommunications system TKS3and a fourth base station BS4 in a fourth telecommunications system TKS4are arranged in a common, third radio area FB3 (radio cell) and can setup telecommunications links to at least one mobile part MT_(3,4).

In order to set up telecommunications links between the base station orstations BS and the mobile parts MT in DECT/GAP systems according toFIGS. 1 to 4, the base station BS (Radio Fixed Part RFP) transmits atregular time intervals via the DECT radio interface, and on simplextransmission paths, the so-called “Dummy Bearer” (first informationcarrier), broadcast information which is received by the mobile part MT(Radio Portable Part RPP) according to FIGS. 1 to 4 and is used by itfor synchronization and for setting up the link to the base station. Thebroadcast information need not necessarily be transmitted via the “DummyBearer”.

It is also possible for no “Dummy Bearer” to be required, because thebase station already maintains at least one telecommunications link, theso-called “Traffic Bearer” (second information carrier) to anothermobile part, on which it then transmits the necessary broadcastinformation. In this case, the mobile part which would like to have atelecommunications link to a base station can receive the broadcastinformation as if said broadcast information were transmitted via the“Dummy Bearer”.

According to the ETSI publication ETS 300175-3, October 1992, Section9.1.1.1, the broadcast information contains information about accessrights, system information and paging information.

The system information furthermore contains additional information whichinforms the mobile part of the TDMA time slots which are available atthe base station. In the DECT Standard (ETSI Publication ETS 300175-3,October 1992, Section 11.4.1, Note 4) and the GAP Standard which is asubset of the DECT Standard and has the task of ensuringinteroperability of the DECT radio interface for telephone applications(see ETSI Publication prETS 300444, April 1995, Section 10.3.3), thisadditional information is called “Blind Slot” information or “PoorChannel” information. The transmission of the additional information isbased on the “Blind Slot Effect” which occurs in TDMA/FDMA radiosystems, like the DECT system. The “Blind Slot Effect” occurs inparticular when

a) base stations according to FIG. 2 each have only one radio part withone transmitter and receiver and can thus transmit or receive on onlyone frequency during a time slot; if the base station maintains a duplexradio link in a specific pair of time slots, then it cannot set up anyfurther radio links to other mobile parts in this pair of time slots;

b) base stations according to PCT Reference WO 94/10811 cannot transmitor receive in certain time slots because of technical restrictions (forexample DECT base stations with a “Slow Hopping” radio part).

Case b) is irrelevant in the following text since the present inventionis based on base stations having a fast channel changing function (FHbase stations).

Links are set up in accordance with the rules of channel selection (seeETSI Publication ETS 300175-3, October 1992, Section 11.4), according towhich a new channel is selected for setting up a new link and theconnection request (SETUP request) is transmitted. The channel selectionis in this case carried out essentially in the central controller ZST ofthe mobile part MT or of the base station BS according to FIG. 2.

The “Blind Slot Effect” which has been explained above in the context ofthe base station BS also occurs, of course, in the mobile part MT; thisarises, in particular, when

a) mobile parts according to FIG. 2 each have only one radio part withone transmitter and receiver and can thus transmit or receive at onlyone frequency during a time slot; if the mobile part maintains a duplexradio link to a base station in a specific pair of time slots, then itcannot set up any further radio links to another base station in thispair of time slots;

b) mobile parts according to PCT Reference WO 94/10811 cannot transmitor receive in certain time slots because of technical restrictions (forexample DECT mobile parts with a “Slow Hopping” radio part).

On the basis of the above statements and the fact that, on the one hand,“Fast Hopping” radio parts are considerably more complex to develop than“Slow Hopping” radio parts and are thus more expensive and, on the otherhand, there is interest in manufacturing the mobile parts ascost-effectively as possible, a scenario results in which the cellularDECT/GAP system according to FIG. 4 contains base stations with a fastchannel changing function (Fh base stations) and mobile parts with aslow channel changing function (SH mobile parts).

In consequence—according to FIG. 5—such a system contains for example anSH mobile part (mobile part with a slow channel changing function)SH-MT_(1,2), which can be connected at the same time to two basestations—an SH base station (base station with a slow channel changingfunction) SH-BS1 and an FH base station (base station with a fastchannel changing function) FH-BS2 or two FH base stations (base stationswith a fast channel changing function) FH-BS1, FH-BS2—bytelecommunication. While the the SH mobile part SH-MT_(1,2) is connectedto a first SH/FH base station SH-BS1, FH-BS1 by telecommunication, theSH mobile part SH-MT_(1,2)—because it is located in the area where theradio areas FB1, FB2 overlap—could at the same time first of all set up,by synchronization, a telecommunications link in spe to a second FH basestation FH-BS2 (keyword: roaming, handover). This synchronization isinitiated by transmitting the broadcast information mentioned above fromthe respective base station to the relevant mobile part. The broadcastinformation can in this case—as already mentioned—be transmitted via a“Dummy Bearer” or a “Traffic Bearer”. For reasons of spectral efficiencyin DECT/GAP systems, not more than, for example, two TDMA time slots(transmission time slots for the respective base station) should be usedfor transmitting the broadcast information. This results in thefollowing problem:

If, for example, the second FH base station FH-BS2 transmits thebroadcast information via a “Dummy Bearer” in the time slots “3” and “5”(for example the first “Dummy Bearer” DB1 in time slot “3” and thesecond “Dummy Bearer” DB2 in time slot “5”) to the SH mobile partSH-MT_(1,2), and if this SH mobile part SH-MT_(1,2) at the same timeuses a “Traffic Bearer” TB to maintain a telecommunications link to thefirst SH/FH base station SH-BS1, FH-BS1 in the time slot “4”, then theSH mobile part SH-MT_(1,2)—as a result of the fact that, because of theSH radio part, it cannot change from an active time slot to adjacenttime slots when a frequency change takes place—cannot receive thebroadcast information transmitted from the second FH base station FH-BS2(“Blind Slots” Effect).

FIG. 6 uses a time slot allocation table to show that the SH mobile partSH-MT_(1,2) is “blind” for signals which the second FH base stationFH-BS2 transmits in the time slots “3” to “5”. Because of the “TrafficBearer” TB, the SH mobile part SH-MT_(1,2) cannot receive anything inthe time slot “4” and, because of the SH radio part, the SH mobile partSH-MT_(1,2) cannot receive the “Dummy Bearers” DB1, DB2 in the timeslots “3” and “5”.

SUMMARY OF THE INVENTION

The object on which the invention is based is to make it possible for amobile part with a slow channel changing function to be synchronized ina manner which is economic in terms of frequencies and, at the sametime, to at least two base stations—for example to two base stationshaving a fast channel changing function—in a cellular TDMA/FDMA radiosystem, in particular a cellular DECT/GAP system.

In general terms the present invention is a base station having a fastchannel changing function in a cellular TDMA/FDMA radio system, inparticular in a cellular DECT/GAP system. At least one base stationhaving a fast channel changing function is arranged in radio cells ofthe cellular TDMA/FDMA radio system. A first radio module can beswitched to any frequency of the TDMA/FDMA radio system. The basestation can be connected by telecommunication to a mobile part having aslow channel changing function of the TDMA/FDMA. The base station emitsinformation carriers. In order to receive the information carriers, themobile part has a second radio module which includes a receiveseparation which occupies a first number “n” of TDMA time slots where“n≧2”. A means for forming a pair of information carriers has a firstinformation carrier and/or a second information carrier. These aredesigned such that a transmit separation, which occupies a second number“m” of TDMA time slots, between the two information carriers of the pairof information carriers is greater than the receive separation of thesecond radio module. The means are connected to the first radio modulein order to transmit the pair of information carriers.

Advantageous developments of the present invention are as follows.

The transmit separation between the two information carriers of the pairof information carriers occupies three TDMA time slots. The receiveseparation between the two information carriers of the pair ofinformation carriers occupies two TDMA time slots.

The mobile part which can be connected to the base station bytelecommunication, is located in a region where the radio cells overlapor intersect.

The first information carrier is a “Dummy Bearer”.

The second information carrier is a “Traffic Bearer”.

A DECT-specific base station in a DECT system, which base station can beconnected to a DECT-specific mobile part by telecommunication.

The idea on which the invention is based is that a base station having afast channel changing function in a cellular TDMA/FDMA radio system, inparticular a cellular DECT/GAP system, transmits broadcast informationto a mobile part having a slow channel changing function in the radiosystem, which already maintains a telecommunications link to anotherbase station in the radio system, in a predetermined transmit separationwhich is defined as a number of TDMA time slots and is greater than areceive separation which is predetermined by a slow channel changingfunction in the mobile part and is defined as a number of TDMA timeslots.

The transmit separation is in this case preferably determined by aprogram module in the central controller of the base station.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention which are believed to be novel,are set forth with particularity in the appended claims. The invention,together with further objects and advantages, may best be understood byreference to the following description taken in conjunction with theaccompanying drawings, in the several Figures of which like referencenumerals identify like elements, and in which:

FIG. 1 depicts a monocellular DECT/GAP system;

FIG. 2 depicts the base station and mobile part;

FIG. 3 depicts the TDMA structure of the FIG. 1 system;

FIG. 4 depicts a cellular DECT/GAP multi-system cordless multi-cellintegration;

FIG. 5 depicts a system having a mobile part with a slow channelchanging function;

FIG. 6 depicts a time slot allocation table;

FIG. 7 depicts a second base station and mobile part;

FIG. 8 depicts relationships for transmission of broadcast information;and

FIG. 9 depicts further relationships for transmission of broadcastinformation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 7 is based on FIGS. 2 and 5 and shows the basic circuit layout ofthe second FH base station (base station having a fast channel changingfunction) FH-BS2 and of the SH mobile part (mobile part having a slowchannel changing function) SH-MT_(1,2). This circuit layout and thefollowing statements also apply to the first FH base station FH-BS1,which may be designed (see the description relating to FIG. 5) as an FHbase station. In the case of SH mobile part SH-MT_(1,2), the radio partFKT which is illustrated in FIG. 2 is designed as an SH radio partSH-FKT which cannot change from an active time slot to adjacent timeslots during a frequency change. Instead of this, the SH radio partSH-FKT can first change to the respective next-but-one time slot. Thereceive separation of the SH radio part SH-FKT is thus a first number(n) of time slots where “n≧2”. In the present exemplary embodiment“n=2”.

In the second FH base station FH-BS2, the radio part FKT which isillustrated in FIG. 2 is designed as an FH radio part FH-FKT which canchange from an active time slot to adjacent time slots during afrequency change. In addition, the central controller ZST of the secondFH base station FH-BS2 has an additional program module PGM_(z), whichis designed in such a manner that, taking account of the spectralefficiency in a DECT/GAP system, the SH mobile part SH-MT_(1,2) can inall cases receive the broadcast information transmitted from the FH basestation FH-BS2 according to FIG. 5.

CASE I

If—as illustrated in FIGS. 5 and 6—the second base station FH-BS2transmits the broadcast information via the two “Dummy Bearers” DB1, DB2in the course of channel selection—the first “Dummy Bearer” DB1 beingpositioned, for example,—as shown in FIGS. 5 and 6—in time slot “3”,then the program module PGM_(z) ensures that the second “Dummy Bearer”DB2 is positioned in a time slot which is offset by a second number (m)of time slots, where “m>n”, from the time slot “3” for the first “DummyBearer” DB1. In the present exemplary embodiment, “m=±3” (see FIGS. 8and 9).

CASE II

If the second base station FH-BS2 transmits the broadcast informationvia a “Dummy Bearer”, for example the first “Dummy Bearer” DB1 in thecourse of channel selection, which “Dummy Bearer” DB1 is positioned, forexample,—as illustrated in FIGS. 5 and 6—in time slot “3”, and if, inaddition, a further time slot is intended to be activated for a “TrafficBearer” TB, then the program module PGM_(z) ensures—if possible—that the“Traffic Bearer” is positioned in a time slot which is offset by thesecond number (m) of time slots, where “m>n”, from the time slot “3” forthe first “Dummy Bearer” DB1. In the present exemplary embodiment,“m=±3” (see FIGS. 8 and 9).

If the “Traffic Bearer” can be positioned in such a time slot, then thetime slot “3” for the first “Dummy Bearer” DB1 can be deactivated. Ifnot, the first “Dummy Bearer” DB1 must be moved to a time slot which isappropriate for transmitting the broadcast information.

CASE III

If the broadcast information is not transmitted from the second basestation FH-BS2 via a “Dummy Bearer” in the course of channel selectionand if a time slot is intended to be activated for a new “TrafficBearer”, then the program module PGM_(z) ensures—if possible—that thenew “Traffic Bearer” is positioned in a time slot which is offset by thesecond number (m) of time slots, where “m>n”, from a time slot for analready existing (old) “Traffic Bearer”. In the present example, “m=±3”(see FIGS. 8 and 9).

If the new “Traffic Bearer” can be positioned in such a time slot, thenthe broadcast information is transmitted in this time slot. Otherwise, a“Dummy Bearer” must be moved to a time slot which is appropriate fortransmitting the broadcast information.

Based on FIGS. 5 and 6, FIGS. 8 and 9 show the relationships, inconjunction with the transmission of broadcast information, for thecases explained by the description of FIG. 7.

The invention is not limited to the particular details of the apparatusdepicted and other modifications and applications are contemplated.Certain other changes may be made in the above described apparatuswithout departing from the true spirit and scope of the invention hereininvolved. It is intended, therefore, that the subject matter in theabove depiction shall be interpreted as illustrative and not in alimiting sense.

What is claimed is:
 1. A base station having a fast channel changingfunction in a cellular TDMA/FDMA radio system, comprising: the basestation which has a fast channel changing function being in radio cellsof the cellular TDMA/FDMA radio system; a first radio module that isswitchable to any frequency of the TDMA/FDMA radio system; the basestation being connectable by telecommunication to a mobile part having aslow channel changing function of the TDMA/FDMA; the base stationemitting information carriers, whereby, in order to receive theinformation carriers, the mobile part has a second radio module whichincludes a receive separation which occupies a first number “n” of TDMAtime slots where n≧2; a device for forming a pair of informationcarriers, the pair of information carriers having at least one of afirst information carrier and a second information carrier, such that atransmit separation, which occupies a second number “m” of TDMA timeslots, between the first and second information carriers of the pair ofinformation carriers is greater than a receive separation of the secondradio module; the device connected to the first radio module in order totransmit the pair of information carriers.
 2. The base station accordingto claim 1, wherein the transmit separation between the first and secondinformation carriers of the pair of information carriers occupies threeTDMA time slots, and wherein the receive separation between the firstand second information carriers of the pair of information carriersoccupies two TDMA time slots.
 3. The base station according to claim 1,wherein the mobile part which is connectable to the base station bytelecommunication, is located in a region where the radio cells overlapor intersect.
 4. The base station according to claim 1, wherein thefirst information carrier is a “Dummy Bearer”.
 5. The base stationaccording to claim 1, wherein the second information carrier is a“Traffic Bearer”.
 6. The base station according to claim 1, wherein thebase station is a DECT-specific base station in a DECT system, whichbase station is connectable to a DECT-specific mobile part bytelecommunication.
 7. The base station according to claim 1, wherein thecellular TDMA/FDMA radio system is a cellular DECT/GAP system.